Buying the Baltimore-based BCSB will give FNB an additional $640 million in assets and 16 banking offices in the greater Baltimore area. FNB currently operates in three major metropolitan areas: Pittsburgh, Baltimore and Cleveland, with about 250 banking offices in Pennsylvania, Ohio, West Virginia and Maryland. It has $12.4 billion in assets.

FNB expects that in the first year after the acquisition, it will get a slight bump in earnings per share when excluding one-time costs.

Both companies' boards have approved the deal, which is anticipated to close in the first quarter of 2014. The acquisition still needs the approval of BCSB shareholders.